5.2.6.1. AMR

For a description of the general AMR process, see “Using Adaptive Mesh Refinement (AMR)”. RF3p supports two AMR modes:
Ports Only, in which the simulation is confined to extracting modes
at wave ports, and Full, in which the simulation is performed on the
total volume of the problem. Independent control of error tolerance and number of
iterations for each mode is provided. The ports only AMR process is only required for wave
ports; lumped ports are defined according to a simple analytical model and don't require a
separate eigensolution. For wave ports, the field solution on the port is the source for
the volumetric simulation; it is therefore important to ensure the ports only AMR proceeds
appropriately. The same methods are used to ensure performance of the ports only AMR and
the full solve AMR, as follows.

When a simulation spans multiple frequencies, the most fastidious AMR process would
compute the solution for all frequencies in each AMR step. Usually, however, this is both
unacceptably cumbersome and wholly unnecessary. In general, the mesh obtained from a
single-frequency AMR process will yield accurate results over a spectrum of frequencies.
In the simulation properties dialog box under the AMR Sequence tab,
you may choose the AMR frequency by choosing a value for Frequency
Modifier, which allows selection of predefined options. Most of the time the
default selection, Mid, is sufficient, which corresponds to a
frequency in the middle of the band. If widely varying or discontinuous behavior is
expected over the range of simulation frequencies for a particular system, other choices
may be more appropriate. In addition, you can choose a custom frequency from the set of
frequencies at which your problem is to be solved. As an example, the simulation of a band
pass filter may require use of a custom frequency, if the High,
Low, and Mid frequencies are not in the band
pass region. If All is chosen, the AMR sequence will usually take
significantly longer to converge.

In the ports only AMR, the convergence criterion is based upon the characteristic
impedance Zc for each of the modes.

In the full solve AMR, you can choose to base convergence on ΔS, i.e. the maximum
change in the magnitude of the scattering matrix S, or you can choose to base convergence
on both ΔS and Δϕ, the maximum change in the phase of S (across all AMR frequencies and
all terms in S). In the latter case you can set a cutoff magnitude below which the phase
change is ignored.

At each new AMR step, RF3p calculates an estimate of the memory
needed for the step. If it determines that further iterations will cause you to run out of
memory, it aborts the AMR process with an appropriate message and moves to the final
solve, described in “Running”. You should get results if
this occurs, but the results are not fully converged and they should be used with caution.